(230y) Shear-Induced Structural Changes in Electrostatically Gelled Nanoparticle Dispersions

Mixtures of oppositely-charged fumed metal oxide nanoparticles will heteroaggregate into a fluid spanning network when dispersed in water. The gels produced by this process exhibit a yield stress at nanoparticle volume fractions greater than 0.015. Phase behavior studies and corresponding rheological characterization have demonstrated that the nanoparticle network only exists when the solution pH is in the range where the different nanoparticle species have opposite surface charges. Additionally, the strongest gel networks, i.e. the gels with the highest yield stress, were formed at particle ratios where the number of positive and negative surface charges are approximately equal. This work uses small angle neutron scattering to characterize the structure of the gel network in binary mixtures of fumed silica (SiO₂) and fumed alumina (Al₂O₃) and how it evolves under flow. Static gels were characterized at various particle concentrations, solution pHs, and mixture ratios. RheoSANS and RheoUSANS is used to investigate how the gel networks respond under flow and gain insight into network rearrangements and shear-induced phase separation at certain shear rates.